Braking distance

[smilestar]

Hello all,

Which is the correct formula for braking distance. I have sometimes seen -30 used in the formula, is that correct.

1. Db= (vf^2 – vi^2)/ 30(f + G)

2. Db= (vf^2 – vi^2)/ - 30(f + G)

Thanks for your help.

 

[John QPE]

It varies on whether or not you are given the coefficient of friction or not, and this only applies to uneven ground. Your velocities are backwards too.

db = {1.075(Vi2 - Vf2) / a+ 0.32G% if given acceleration and vertical grade

db = Vi2 - Vf2 / 30 (f + G) if given coefficient of friction and grade

 

[ptatohed]

Hello all,

Which is the correct formula for braking distance. I have sometimes seen -30 used in the formula, is that correct.

1. Db= (vf^2 – vi^2)/ 30(f + G)

2. Db= (vf^2 – vi^2)/ - 30(f + G)

Thanks for your help.

You should not use -30. It should be positive 30. And the +/- before the grade is + for uphill, - for downhill. Also, don't forget, this does not include reaction distance. Add 1.47 V t for total SSD.

It varies on whether or not you are given the coefficient of friction or not, and this only applies to uneven ground. Your velocities are backwards too.

db = {1.075(Vi2 - Vf2) / a+ 0.32G% if given acceleration and vertical grade

db = Vi2 - Vf2 / 30 (f + G) if given coefficient of friction and grade

Yup, f = a / g

 

[smilestar]

Thank you guys, but I am still confused. I am looking at six minute solution # 64. The problem asked to calculate the skid distance.

It uses Db= (vf^2 – vi^2)/ 30(f + G) for the first part of the skid.

And then uses Db= (vf^2 – vi^2)/ 30(f + G) for the second part of the skid which is on grass.

If somebody can help clarify that would be great, is the formula in 6 minute wrong?

Thanks a lot

 

[ptatohed]

Thank you guys, but I am still confused. I am looking at six minute solution # 64. The problem asked to calculate the skid distance.

It uses Db= (vf^2 – vi^2)/ 30(f + G) for the first part of the skid.

And then uses Db= (vf^2 – vi^2)/ 30(f + G) for the second part of the skid which is on grass.

If somebody can help clarify that would be great, is the formula in 6 minute wrong?

Thanks a lot

ss,

What are you questioning? That PPI's equation is final velocity minus initial velocity, and not vice versa? I agree with JQ that it should be vi - vf, but written as you show it, doesn't it just give a negative answer? But still the correct distance? Really, the value 'a' in the equation should be negative in my opinion since it's a deceleration (not acceleration). So, thought of that way, negative divided by negative is positive. Are you getting the right distance value for the answer, just negative? Or is there another issue?

 

[Dexman PE PMP]

What if I upgrade my front brake calipers to the larger 6-piston versions and upgrade springs?

 

[smilestar]

@ ptatohed, yes I am getting the right answer. I just wanted to make sure I am using correct eqn, since I saw both versions (vf^2 - vi^2) and (vi^2-vf^2).

I understand what you saying, the equation John wrote takes care of negative sign for deceleration, that's what I was thinking too, deceleration should be negative.

Thanks for helping guys.